1. Field of the Invention
The present invention relates generally to a plasma processing apparatus and system, a performance evaluation method therefor, a maintenance method therefor, a performance management system therefor, and a performance validation system therefor. More particularly, the present invention is directed to a technology suitable for ensuring that the plasma processing apparatus and system maintain the required level of performance even after the delivery of the apparatus and system to customers.
2. Description of the Related Art
FIG. 38 illustrates an example of a conventional dual-frequency excitation plasma processing apparatus which performs a plasma process such as a chemical vapor deposition (CVD) process, a sputtering process, a dry etching process, or an ashing process.
In the plasma processing apparatus shown in FIG. 38, a matching circuit 2A is connected between a radiofrequency generator 1 and a plasma excitation electrode 4. The matching circuit 2A matches the impedances of the radiofrequency generator 1 and the excitation electrode 4.
Radiofrequency power from the radiofrequency generator 1 is fed to the plasma excitation electrode 4 via the matching circuit 2A and a feed plate 3. The matching circuit 2A is accommodated in a matching box 2 which is a housing composed of a conductive material. The plasma excitation electrode 4 and the feed plate 3 are covered by a chassis 21 made of a conductor.
The plasma excitation electrode 4 is provided with a projection 4a at the bottom face thereof. A shower plate 5 having many holes 7 provided under the plasma excitation electrode 4 is in contact with the projection 4a. The plasma excitation electrode 4 and the shower plate 5 define a space 6. A gas feeding tube 17 composed of a conductive material is connected to the space 6. The gas feeding tube 17 is provided with an insulator 17a at the middle thereof so as to insulate the plasma excitation electrode 4 and the gas source.
Gas from the gas feeding tube 17 is fed inside a plasma processing chamber 60 comprising a chamber wall 10, via the holes 7 in the shower plate 5. An insulator 9 is disposed between the chamber wall 10 and the plasma excitation electrode 4 (cathode) to provide insulation therebetween. The exhaust system is omitted from the drawing.
A wafer susceptor (susceptor electrode) 8 which receives a substrate 16 and also serves as another plasma excitation electrode is installed inside the plasma processing chamber 60. A susceptor shield 12 is disposed under the wafer susceptor 8.
The susceptor shield 12 comprises a shield supporting plate 12A for supporting the susceptor electrode 8 and a supporting cylinder 12B extending downward from the center of the shield supporting plate 12A. The supporting cylinder 12B extends through a chamber bottom 10A, and the lower portion of the supporting cylinder 12B and the chamber bottom 10A are hermetically sealed with bellows 11.
The shaft 13 and the susceptor electrode 8 are electrically isolated from the susceptor shield 12 by a gap between the susceptor shield 12 and the susceptor electrode 8 and by insulators 12C provided around the shaft 13. The insulators 12C also serve to maintain high vacuum in the plasma processing chamber 60. The susceptor electrode 8 and the susceptor shield 12 can be moved vertically by the bellows 11 in order to control the distance between plasma excitation electrodes 4 and 8.
The susceptor electrode 8 is connected to a second radiofrequency generator 15 via the shaft 13 and a matching circuit accommodated in a matching box 14. The chamber wall 10 and the susceptor shield 12 have the same DC potential.
FIG. 39 illustrates another example of a conventional plasma processing apparatus. Unlike the plasma processing apparatus shown in FIG. 38, the plasma processing apparatus shown in FIG. 39 is of a single-frequency excitation type. In other words, a radiofrequency power is supplied only to the electrode 4 while the susceptor electrode 8 is grounded. Moreover, the matching box 14 and the second radiofrequency generator 15 shown in FIG. 38 are not provided. The susceptor electrode 8 and the chamber wall 10 have the same DC potential.
In these plasma processing apparatuses, power with a frequency of approximately 13.56 MHz is generally supplied in order to generate a plasma between the electrodes 4 and 8. A plasma process such as a plasma-enhanced CVD process, a sputtering process, a dry etching process, or an ashing process is then performed using the plasma.
The power consumption efficiency, i.e., the ratio of the power consumed in the plasma to the power supplied to the plasma excitation electrode 4, of these plasma processing apparatuses has been poor. Especially as the frequency supplied from the radiofrequency generator is elevated, the power consumption efficiency of the plasma processing apparatus has decreased significantly. Moreover, use of large size substrates has caused the power consumption efficiency to further decrease.
As a result, conventional plasma processing apparatuses have suffered from low deposition rate as a result of failing to increase the effective power consumed in the plasma space due to a low power consumption efficiency. When applied to a deposition process, for example, insulating layers with high isolation voltage can barely be formed.
The operation validation and performance evaluation of the above-described plasma processing apparatuses have been conducted by actually performing the process such as deposition and then evaluating the deposition characteristics thereof according to following Procedures:
Procedure (1) Deposition Rate and Planar Uniformity
Step 1: Depositing a desired layer on a 6-inch substrate by a plasma-enhanced CVD process.
Step 2: Patterning a resist layer.
Step 3: Dry-etching the layer.
Step 4: Removing the resist layer by ashing.
Step 5: Measuring the surface roughness using a contact displacement meter to determine the layer thickness.
Step 6: Calculating the deposition rate from the deposition time and the layer thickness.
Step 7: Measuring the planar uniformity at 16 points on the substrate surface.
Procedure (2) BHF Etching Rate
A resist mask is patterned as in Steps 1 and 2 in (1) above.
Step 3: Immersing the substrate in a buffered hydrofluoric acid (BHF) solution for one minute to etch the layer.
Step 4: Rinsing the substrate with deionized water, drying the substrate, and separating the resist mask using a mixture of sulfuric acid and hydrogen peroxide (H2SO4+H2O2).
Step 5: Measuring the surface roughness as in Step 5 in Procedure (1) to determine the layer thickness after the etching.
Step 6: Calculating the etching rate from the immersion time and the reduced layer thickness.
Procedure (3) Isolation Voltage
Step 1: Depositing a conductive layer on a glass substrate by a sputtering method and patterning the conductive layer to form a lower electrode.
Step 2: Depositing an insulating layer by a plasma-enhanced CVD method.
Step 3: Forming an upper electrode as in Step 1.
Step 4: Forming a contact hole for the lower electrode.
Step 5: Measuring the current-voltage characteristics (I-V characteristics) of the upper and lower electrodes by using probes while applying a voltage up to approximately 200 V.
Step 6: Defining the isolation voltage as the voltage V at 100 pA corresponding 1 μA/cm2 in a 100 μm square electrode.
The plasma processing apparatus for use in manufacturing semiconductors and liquid crystal displays has been required to achieve a higher plasma processing rate (the deposition rate or the processing speed), increased productivity, and improved planar uniformity of the plasma processing (uniformity in the distribution of the layer thickness in a planar direction and uniformity in the distribution of the process variation in the planar direction). As the size of substrates has been increasing in recent years, the requirement of planar uniformity has become tighter.
Moreover, as the size of the substrate is increased, the power required is also increased to the order of kilowatts, thus increasing the power consumption. Accordingly, as the capacity of the power supply increases, both the cost for developing the power supply and the power consumption during the operation of the apparatus are increased. In this respect, it is desirable to reduce the operation costs.
Furthermore, an increase in power consumption leads to an increase in emission of carbon dioxide which places a burden on the environment. Since the power consumption is increased by the combination of increase in the size of substrates and a low power consumption efficiency, reduction of the carbon dioxide emission is desired.
The power consumption efficiency is known to be improved by increasing the plasma excitation frequency. For example, a frequency in the VHF band of 30 MHz or more can be used to improve the efficiency instead of the conventional 13.56 MHz. Thus, one possible way to improve the deposition rate of a deposition apparatus such as a plasma-enhanced CVD apparatus is to employ a higher plasma excitation frequency.
In a plasma processing apparatus having a plurality of the above-described plasma processing chambers, i.e., a multi-chamber plasma processing apparatus, variation in plasma processing among the plasma processing chambers is required to be reduced so that the plasma processing rate (deposition rate when applied to a deposition process), productivity, and uniformity in the plasma process in the planar direction of a workpiece (planar distribution in the layer thickness) can be made substantially the same among the workpieces plasma-treated in different plasma processing chambers.
The plasma processing apparatus is also required to yield substantially the same process results by applying the same process recipe specifying external parameters for respective plasma processing chambers such as gas flow, gas pressure, power supply, and process time.
During installation or maintenance of the plasma processing apparatus, reduction in the time required for adjusting the plasma processing apparatus to achieve substantially the same process results by applying the same recipe and eliminate the variation among the plurality of plasma processing chambers has been desired. Also, reduction in the cost required for such adjustment has been desired.
Furthermore, in a plasma processing system comprising a plurality of plasma processing apparatuses, improvement in the uniformity in plasma process results among the plasma processing chambers of the apparatuses has also been desired.
The above-described plasma processing chamber is designed to use power with a frequency of approximately 13.56 MHz and is not suited for power of higher frequencies. Specifically, radiofrequency characteristics such as capacitance, impedance, and resonant frequency characteristics of the plasma processing chamber as a whole have been neglected; consequently, no improvement in the electrical consumption efficiency has been achieved even when power of a frequency higher than approximately 13.56 MHz is employed, resulting in decrease in the deposition rate rather than improvement. Moreover, although the effective power consumed in the plasma space increases as the frequency increases, the effective power starts to decrease once its peak value is reached, eventually reaching a level at which glow-discharge is no longer possible, thus rendering further increases in frequency undesirable.
Conventional plasma processing apparatuses suffer from the following disadvantages.
Conventional plasma processing apparatuses and systems are not designed to eliminate the differences in electrical radiofrequency characteristics such as impedance and resonant frequency characteristics among the plasma processing chambers constituting the plasma processing apparatus or system. Thus, the effective power consumed in the plasma generating spaces of the plasma processing chambers varies between different plasma processing chambers.
As a consequence, uniformity in plasma process results are barely achieved even when the same process recipe is applied to these plasma processing chambers.
In order to obtain uniform plasma process results, external parameters such as gas flow, gas pressure, power supply, process time, and the like must be compared with the process results according to Procedures (1) to (3) described above for each of the plasma processing chambers so as to determine the correlation between them. However, the amount of data required in such a process is enormous and it is impossible to completely carry out the comparison.
Moreover, in order to validate and evaluate the operation of the plasma processing apparatus using Procedures (1) to (3) above, the plasma processing apparatus needs to be operated and deposited substrates need to be examined by an ex-situ inspecting method requiring many steps.
Such an inspection requires several days to several weeks to yield evaluation results, which is significantly long especially when the apparatus is still in development stage. Reduction in time required for obtaining the results has been desired.
Moreover, when Procedures (1) to (3) described above are employed to inspect the plasma processing units constituting the plasma processing apparatus or system, the time required for adjusting the plasma processing units so as to eliminate the difference in performance and variation in processing among the plasma processing chambers to achieve the same process results using the same process recipe may be months. The time required for such adjustment needs to be reduced. Also, the cost of substrates for inspection, the cost of processing the substrates for inspection, the labor cost for workers involved with the adjustment, and so forth are significantly high.
As described above, while the plasma processing apparatus is required to achieve a desired performance level, a multi-chamber plasma processing apparatus and a plasma processing system having the plurality of plasma processing chambers are required to eliminate the differences in the performance of plasma process among the plurality of plasma processing chambers.
Even if the plasma processing apparatus has once been optimized as above, the plasma processing apparatus is generally disassembled before the transfer and then reassembled at the customer site. Thus, it is possible that the performance is not maintained at the level maintained before the transfer due to the vibration during the transfer and inappropriate reassembly work.
Moreover, the performances of the plasma processing chambers would deviate from the required performance level and would exhibit variation in the performance among the plasma processing chambers as plasma processes are repeated in the plasma processing apparatus after reassembly of the plasma processing apparatus. Also, when an adjustment work such as overhaul, parts replacement, and assembly with alignment is performed, the plasma processing apparatus may not be maintained at a desired level due to inappropriate adjustment or the like.
When Procedures (1) to (3) described above are employed to evaluate whether the operation of the plasma processing apparatus and the difference among the plasma processing chambers are maintained within the required levels, it becomes necessary to actually operate the plasma processing apparatus and to examine the treated substrates using an ex-situ inspection method requiring a plurality of steps.
If the performance of the plasma processing apparatus does not satisfy the required levels, long series of cycle of adjusting the plasma processing apparatus, performing a plasma process on a substrate, and evaluating the processed substrate needs to be repeated, thereby extending the initialization process of the delivered plasma processing apparatus. The length of the time required to complete the initialization process of a production line directly affects the annual sales.
Thus, it is desired that the validation of the performance of the plasma processing apparatus be performed more easily and that the cycle of fault detection and performance of corrective action be performed in a shorter period of time, so as to shorten the initialization process of the plasma processing apparatus.